A dew pond is an artificial pond usually sited on the top of a hill, intended for watering livestock. Dew ponds are used in areas where a natural supply of surface water may not be readily available. The name dew pond (sometimes cloud pond or mist pond) is first found in the Journal of the Royal Agricultural Society in 1865. Despite the name, their primary source of water is believed to be rainfall rather than dew or mist. If the pond's temperature is kept low, evaporation (a major water loss) may be significantly reduced, thus maintaining the collected rainwater.
They are usually shallow, saucer-shaped and lined with puddled clay, chalk or marl on an insulating straw layer over a bottom layer of chalk or lime. To deter earthworms from their natural tendency of burrowing upwards, which in a short while would make the clay lining porous, a layer of soot would be incorporated or lime mixed with the clay. The clay is usually covered with straw to prevent cracking by the sun and a final layer of chalk rubble or broken stone to protect the lining from the hoofs of sheep or cattle.
A method of constructing the base layer using chalk puddle was described in The Field 14 December 1907. A Sussex farmer born in 1850 tells how he and his forefathers made dew ponds: “The requisite hole having been excavated, the chalk was laid down layer by layer, while a team of oxen harnessed to a heavy broad-wheeled cart was drawn round and round the cup shaped hole to grind the chalk to powder. Water was then thrown over the latter as work progressed, and after nearly a day of this process, the resultant mass of puddled chalk, which had been reduced to the consistency of thick cream, was smoothed out with the back of a shovel from the centre, the surface being left at last as smooth and even as a sheet of glass. A few days later, in the absence of frost or heavy rain, the chalk had become as hard as cement, and would stand for years without letting water through. This old method of making dew ponds seems to have died out when the oxen disappeared from the Sussex hills, but it is evident that the older ponds, many of which have stood for scores of years practically without repair, are still more watertight than most modern ones in which Portland cement has been employed.” 
The mystery of dew ponds has drawn the interest of many historians and scientists, but until recent times there has been little agreement on their early origins. It was widely believed that the technique for building dew ponds has been understood from the earliest times, as Kipling tells us in Puck of Pook's Hill. The two Chanctonbury Hill dew ponds were dated, from flint tools excavated nearby and similarity to other dated earthworks, to the neolithic period. Landscape archaeology too seemed to demonstrate that they were used by the inhabitants of the nearby hill fort (probably from an earlier date than that of the surviving late bronze age structure) for watering cattle. A more prosaic assessment from Maud Cunnington, an archaeologist from Wiltshire, while not ruling out a prehistoric origin, describes such positive interpretations of the available evidence as no more than “flights of fancy”. A strong claim to antiquity may, however, be made for at least one Wiltshire dew pond: A land deed dated 825 CE mentions Oxenmere ( ) at Milk Hill, Wiltshire, showing that dew ponds were in use during the Saxon period. In the eighteenth century the naturalist Gilbert White noted that during extended periods of summer drought the artificial ponds on the downs above his native Selborne, Hampshire, retained their water, despite supplying flocks of sheep, while larger ponds in the valley below had dried up. Later observations demonstrated that during a night of favourable dew formation a typical increase in water level of some two or three inches was possible.
There is equal controversy on the means of replenishment of dew ponds. Experiments conducted in 1885 to determine the origin of the water found that dew forms not from dampness in the air but from moisture in the ground directly beneath the site of the condensation: dew, therefore, was ruled out as a source of replenishment. Other scientists have pointed out that the 1885 experiments failed to take into account the insulating effect of the straw and the cooling effect of the damp clay: the combined effect would be to keep the pond at a lower temperature than the surrounding earth and thus able to condense a disproportionate share of moisture. In turn these conclusions were disproved in the 1930s, when it was pointed out that the heat-retaining quality of water (its thermal capacity) was many times greater than that of earth and therefore the air above a pond in summer would be the last place to attract condensation. The deciding factor, it was concluded, is the extent of the saucer-shaped basin extending beyond the pond itself: the large basin would deliver more rainfall than a pond created without such a surrounding feature.
- ↑ Oxford English Dictionary: dew-pond
- ↑ Mayhew, Susan (2004). A Dictionary of Geography: Dew Pond. Oxford, England: Oxford University Press. ISBN 0198606737.
- ↑ Brooks, Alan; Agate, Elizabeth (1976). Waterways and Wetlands. Doncaster: British Trust for Conservation Volunteers. ISBN 0946752303. http://handbooks.btcv.org.uk/handbooks/content/section/2439.
- ↑ 4.0 4.1 Johnson, Walter (1908). Folk Memory Or the Continuity of British Archaeology. Oxford, England: Oxford University Press.
- ↑ Edward A Martin Dew Ponds History observation and Experiment 1915 page 85
- ↑ Edward A Martin Dew Ponds History observation and Experiment 1915 page 84/85
- ↑ Edward A Martin Dew Ponds History observation and Experiment 1915 page 96
- ↑ "...the Flint Men made the Dewpond under Chanctonbury Ring."
- ↑ 9.0 9.1 9.2 Hubbard, Arthur John; Hubbard, George (1905). Neolithic Dew Ponds and Cattleways. London: Longman, Green.
- ↑ "Chanctonbury Ring". Prehistory. Steyning Museum. 2005. http://steyningmuseum.org.uk/chanctonbury.htm. Retrieved 2008-04-14.
- ↑ 11.0 11.1 Cunnington, Maud Elizabeth (1934). An Introduction to the Archæology of Wiltshire from the Earliest Times to the Pagan Saxons. Devizes, England: George Simpson and Co.
- ↑ "Dew ponds". Wiltshire Community History. Wiltshire County Council. http://www.wiltshire.gov.uk/community/getfaq.php?id=47. Retrieved 2008-04-14.
- ↑ White, Gilbert (1788). The Natural History of Selborne. London: Benjamin White and Son.
- ↑ Pugsley, Alfred J (1939). Dewponds in Fable and Fact. London: Country Life Ltd.
- Dew Ponds to the rescue
- 4to40 article about dew ponds[dead link]
- Topline information about Wiltshire dew ponds
- Article about dew ponds in Ascension Island
- Dew pond images at Geograph
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Beckett & Dufton Collection of Dew on Roofs Nature May 11, 1935 p 798
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Pope, A. Some Dewponds in Dorset Dorset County Chronicle Office 1912
Walford, E. The Great Dewpond Myth Discovery Vol V October 1924 p 245
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